Overdrive Problem, 1990 Celica GT-S Options

[soad1125889]

One day last week, I was driving to work and my car (1990 Celica GT-S Automatic) started going in and out of overdrive. I unplugged the overdrive to where you have to manually shift gears but it's not a practical way to drive an automatic. I put in a new throttle position sensor which didn't do anything. I've checked the transmission fluid which was clean. I also read that the overdrive was somehow related to the temperature of the engine so I replaced the thermostat and coolant which also did nothing (temperature gauge seems to be working fine). I have found out the this problem is less likely to occur if it is not hot outside. Usually it is cool outside when I go to work and the overdrive works fine, but it comes back when I have to leave work and it is warm outside. Also when it is idling, the rpms will go up for no reason. My intake hose is bad but I'm not sure if both problems are related to the intake hose. If you have any idea what could be causing this, please post.

Thanks.

[1990 gts bdog]

JUST WONDERING IF YOU HAVE GOTTEN THE PROBLEM FIXED. I ALSO HAVE 1990 GTS AUTO TRANNY SAME PROBLEM. CANT FIND ANY INFO.